Thursday, 27 December 2012

GH3 electronic shutter

One of the interesting new features of the Panasonic GH3 (my review) is the possibility to use an electronic shutter. It's not correct to say that this is a new feature, though, as the Panasonic G5, launched some months earlier, also has an electronic shutter. Probably, these cameras share some sensor components.

The electronic shutter has the advantage of being silent, of course, since no mechanical shutter is moving at all. It probably also has a quicker response time, however, I have not tested if this is actually a fact.

On the downside, the electronic shutter suffers from heavy rolling shutter artefacts, making it virtually unusable with moving subjects, or with a long lens. It also does not work with a flash, and cannot be used with high ISO or a very slow shutter speed. I'll get back to all of this in the article.

Silent operation

As said initially, the electronic shutter is interesting because it is totally silent. Normally, when making an exposure with the mechanical shutter, what happens when you press the shutter is this:

The camera focuses (unless you have selected manual focus, MF)

The camera stops down the aperture, unless you have set the largest aperture

The mechanical shutter closes, and the sensor is made ready for an exposure

Finally, what makes the most noise, is the mechanical shutter. Probably because it travels very fast. With the electronic shutter mode, you avoid this noise. Since it is so dominating, most people probably don't notice the noise of the aperture change, anyway.

When using the electronic shutter mode, the camera skips steps 3-6 in the above list.

For the ultimate in silent operation, I took this image, out of a series of exposures, using the Lumix X 12-35mm lens at 12mm f/2.8. When using the maximum aperture, the lens does not change the aperture before the exposure, and there is no noise whatsoever, beyond the initial autofocus sounds. In retrospect, I could have stopped down the lens some, as I notice that the foreground is a bit out of focus. Probably, the crowd would not have noticed anything anyway:

Also, when not using the mechanical shutter, there is less vibrations, which is good for the stability.

Limitations

The electronic shutter cannot be used with a flash. Not the built in flash, nor an external flash. Not even with the external flash in non-TTL auto mode, or in manual mode.

You cannot use the mode with exposures longer than 1s, or with an ISO higher than 1600.

Due to the latter limitations, one could speculate that the image quality is worse for the electronic shutter. To test this, I took the same picture using both shutter types, both images at ISO 1600 and 1s exposure:

Mechanical shutter

Electronic shutter

And here are 100% crops from both images:

As far as I can tell, the images are identical. So there appears to be no reason to worry about the image quality when using the electronic shutter.

Rolling shutter artefacts

So, the silent and vibrationless operation is the advantage of the electronic shutter. What about the disadvantages?

The rolling shutter artefacts of GH3 video is largely "academic". You only see it when you deliberately try to provoke it, e.g., by excessive horizontal panning during video recording. For normal use, this is not much of a problem.

The electronic shutter rolling effects are a problem with real life use, though. Here is a pair of example images taken using both shutter types, at f=32mm, f/2.8, 1/320s, ISO 800:

Mechanical shutter

Electronic shutter

Setting a faster shutter speed would not help. You would still get the skewed car using the electronic shutter. This is because the speed of the sequential sensor readout is independent of the shutter speed.

Moving subjects is not the only problem with the electronic shutter. Camera shake can also be a big problem. Even if you use a very fast shutter speed, the sequential readout from the sensor will be rather slow. Any camera shake during this time means that the image gets a "wobbly" look.

I was holding the camera at arm's length, to get pronounced effects. Even with a shutter speed of 1/200s, which one would normally think is safe with this lens at 175mm, there are heavy rolling shutter artefacts.

So, in this example, I exaggerated the effect by holding the camera at arm's length. But with normal use, I often note similar effects, although less pronounced.

Measuring the rolling shutter

It's easy to forget that the mechanical shutter is also a rolling curtain type shutter. It just moves so quickly that it behaves like a global shutter for most practical purposes.

We know the speed of the mechanical shutter. The camera's flash sync speed is 1/160s. That is the slowest shutter speed in which the whole sensor is exposed at one time. This means that the shutter curtain travel over the sensor at 1/160s, or probably slightly faster for some margin of error. So let's say around 1/180s as a guesstimate of the mechanical rolling shutter speed.

What about the electronic rolling shutter speed? Based on the example images, we know that it is slow, but just how slow? To measure it, Technic Lego again comes to the rescue.

I made this rotating propeller setup. The yellow propeller rotates exactly nine times faster than the red part to the right. By video recording the rotation, I find that the red part rotates twice per second, meaning that the propeller rotates 18 times per second:

Since the yellow propeller is three-pronged, this means that one single blade passes 54 times per second.

To illustrate what an "ideal" picture would look like, I take an exposure using the mechanical shutter first. It turns out like this, 1/1000s, ISO 6400:

So even using the mechanical shutter, we get some rolling shutter artefacts. We just need a very fast moving item to see it. This reminds us that the mechanical shutter is not a perfect global shutter, in fact, it is also a rolling curtain type shutter.

And based on this image, I can try to estimate the speed of the mechanical shutter. The blade has moved around 30° during the exposure. This is 1/12 of a full circle, and the blade rotates 18 times per second. This makes 1/216s passing during the rolling shutter movement. Since the flash sync speed is 1/160s, my estimate makes sense. The shutter is probably slightly faster than the flash sync speed. So my method appears to have merit.

What remains then, is to photograph the upper part of the propeller using the electronic shutter, and count the number of times it passes during the exposure. Here is one example image, taken at ISO 1600, 1/250s, f/2:

A propeller blade passes just above five times, let's say 5.2 times, just to name an estimate. Knowing that one single blade passes 54 times per second, this means that the electronic exposure takes 1/10s. Hence, the flash sync time using the electronic shutter, if it was possible to use the flash, would have been 1/10s. Which is very, very poor. This is the reason why we get the horrible rolling shutter artefacts.

By the way, this is consistent with an interview I read with some Panasonic engineers. They said that the electronic rolling shutter speed was about 0.1s, which is what I measured as well.

Compared with the GH2 electronic shutter

The Panasonic GH2 also has an electronic shutter option. However, it only gives 4MP images at the maximum. My study here reveals that the rolling shutter properties of the electronic shutter mode is exactly the same as the video mode. Hence, it is my belief that the electronic shutter in the GH2 simply takes the video output. That explains why the resolution of the 4MP images are poor, even for a 4MP image. It also explains why the GH2 could not produce images larger than 4MP when using the electronic shutter: This would have required an additional sensor readout process which was not yet available, until the G5 came along.

Comparison with other systems

The Nikon 1 mirrorless cameras were designed with electronic shutter in mind from the start. The Nikon 1 S1 10MP camera has a 1/60s readout, six times faster than that of the Panasonic GH3. The Nikon 1 J3 14MP camera is even better, with an electronic shutter capable of reading the whole image during 1/80S.

Only the Nikon 1 V2 camera features a mechanical shutter at all, usable when you want to be sure the image comes out without any rolling shutter artefacts. Further, the camera can take full 14MP images at a staggering 60FPS rate using the electronic shutter, opening up for very interesting uses.

From the Sony NEX line, some of the recent cameras, e.g., NEX-5R and NEX-6 have an electronic front curtain shutter. This means that the mechanical shutter is not closed prior to the start of the exposure. The only mechanical shutter is the one which closes when the exposure is stopped, the rear curtain. The advantage is obvious: It reduces the vibrations before the exposure commences, and also reduces the number of mechanical movements overall, while still avoiding the rolling shutter artefacts discussed above.

Conclusion

The electronic shutter feature is very interesting. But it's usefulness is limited, since it requires that both the target and the camera are very still. You must keep the camera still for 1/10s, which is pretty much impossible. However, when photographing organic objects like nature or people, small wobbly effects will probably not be noticed. Photographing geometric objects using the electronic shutter can be a problem, though.

Panasonic is marketing this function to be used for action photography. Here is a part of a screenshot from panasonic.net regarding the Panasonic GH3:

From panasonic.net, image copyright Panasonic

However, I doubt that those images could have been taken using the electronic shutter mode, as the movement would have caused significant wobbling effects. They could be video captures, though, as the video rolling shutter artefacts are much smaller.

Despite this, I think the electronic shutter mode of the GH3 is quite interesting, and I use it a lot myself. Unless you are photographing very square objects, like urban architecture, and especially when using a long lens, it is a very good feature to have.

You could even turn the electronic shutter to your advantage, and use it for creative purposes. Here is a picture of a moving car. Since I used the electronic shutter, it appears to lean backwards, while the rest of the scene is the right way up:

This way, you can recreate the famous photo of a racing car taken in 1913 by Jacques Henri Lartigue using a 4x5 Speed Graphic camera:

The shutter moves relatively slowly on this camera almost 100 years old camera, when compared with modern SLRs, which gives the distortion of the racing car. The distortion is especially visible in the wheels, which appear to be leaning forward. This effect was later copied by cartoonists when they wanted to give the impression of speed.

To get the same effect using the GH3, you need to hold the camera upside down. Otherwise, the car will lean backwards.

Real life example

This picture was taken at dusk, at f=28mm, 1/13s, ISO 1600, f/3.2, with the electronic shutter mode. I was panning with the movement of the car to keep it sharp, while blurring the background:

Since I used the electronic shutter, the background buildings are a bit skewed in this picture. They appear to be leaning to the left. This is due to the rolling shutter effect. Had I used the mechanical shutter, the image would have become exactly the same, except that the buildings in the background would not have been skewed. So, is this effect a problem? Not really. I doubt that many would notice the skewed buildings in the background. Perhaps you could say this even makes the image more lively. So my advice is: Unless you are using a very long lens without a tripod, or taking pictures of architecture, go on and use the electronic shutter.

If I may abuse your expertise on the subject, I'd like to know if the electronic shutter is useful in one very particular situation that has proven quite hard for the GH2: long teles (300mm should do it) on a tripod and relatively low shutter speeds (<1/80s).

This kind of situation has proven to be too much of a challenge for my GH2 and it's mechanical shutter. The lack of light and the 5.6 maximum aperture on my 400mm Sigma mean that a lot of the times I'm working in the 1/100s-1/50s range. I have the camera mounted on a relatively solid tripod, but the mechanical shutter plus the extreme 800mm equivalent FL is enough to blur every photo even when using the 2s/10s timer.

Can you please try the electronic shutter against the mechanical one on a similar setup, with long telephoto, realtively low shutter speed, tripod mount and timed release?

I'd be interested in hearing the results of this as well, although assuming the tripod is actually solid (and the object you're shooting isn't moving), I can't imagine it *not* working--that seems an absolutely ideal situation for an electronic shutter, since it won't introduce any camera shake (when combined with, say, a 2s timer), and the rolling effects shouldn't make any difference at all.

I haven't tried this myself, but just like Marc in the other comment, I cannot see this NOT working. When using the mechanical shutter, there is no shutter movement, hence your camera should be completely stable. Just make sure you use a remote trigger, so that you don't push the camera when starting the exposure.

The aperture will change if you are stopping down the lens. But the aperture change doesn't normally cause as much vibration.

Honestly, I don't know. This is a good question. The J1 only has 10MP, which should be faster to read out from the sensor. But still, I would expect that it shows some rolling shutter. But I haven't heard much about this issue.

Compact cameras have a smaller sensor, and hence, transferring the pixel information to the image processor takes less time. For a large sensor camera, this information is transferred a longer distance, which is why they often exhibit rolling shutter artefacts.

Fredrik: you do know the difference between a global electronic shutter and a "rolling" electronic shutter?

The global electronic shutter exposes all pixels at the same time then saves the charge from the PD when the "shutter" closes. The images is then read out. There are no distortions in the image generated in the output. This all requires an extra transistor in every pixel for sample and hold (and doesn't permit shared pixel designs ... that reduced the tranistor count by half).

The Nikon 1 has the former and the GH3 appearently the latter hences the Nikon 1's wider range of shutter speed and lack of artifacts.

I'm a little confused here, about the 1/10 second shutter speed. That would appear to rule out 25, 30, 50 or 60 fps video recording, unless some very funny tricks were being pulled. Does the lower resolution of video help here? and if so why, doesn't the physical sensor have the same number of elements that must be read?

I'm still confused by this. If the readout speed is 1/10th sec for still images what additionally does the camera do to enable you to select 1/125sec or 1/500sec as a shutter speed and prevent the image being over exposed with a 1/10th sec exposure time.

1/10s is the time the camera spends reading out the image values from the entire sensor. However, each row can still be exposed for a shorter time. With 1/500s shutter speed, it means that each pixel row is exposed for 1/500s. However, they are not exposed at the same time. Exposing all the pixel rows is done over a period of 1/10s.

Just think of it as reading a page in a book, or even this web page. The whole page is exposed to you during some period of time (1/10th of a second), but you read each line in a much shorter period (1/500 s). (You even _have_ to do so in order to be able to read the whole page in one tenth of a second.

Thank you for another very helpful article!In addition to the rolling shutter effect, there is another issue using the electronic shutter under artificial lighting. If the shutter speed is not in sync with the frequency of the flicker from the artificial lighting (such as flourescent light bulbs or computer/television screens) one will get clearly visible banding effects in the pictures taken. See also

http://forums.dpreview.com/forums/thread/3362961

To avoid this, one can use a shutter speed in sync with the flicker of the light, for example 1/50 sec in Europe and 1/60 sec in the US. Computer displays running at other refresh rates may require different shutter speeds to eliminate banding.

No, the new "silent mode" just makes the electronic shutter mode more easily available. It does not change the properties of the electronic shutter at all. The electronic shutter still has the same rolling shutter properties.

Thanks for the most in depth review of the electronic shutter mode that I have been able to find on the net. I own three Nikon V1's because they are silent when shooting theater and classical music events.Was hoping that the GH3 would be able to function in this capacity as well with better image quality, however, the thought of looking at the crooked arms of string players does not sound very appealing. I literally had this camera in my cart at Amazon. I will reconsider.

The thing about the GH3 electronic shutter is that you cannot always trust it. It could be that you move the camera slightly, and get skewed vertical lines. Or that the subject moves, for example string players' hands, and looks strange. If you are using a tripod, and have slow moving subjects, then no problem. But for general, daily use, you cannot trust that the images come out perfectly.

Thanks again for the head's up. I am frequently in the back of the room with a 400mm 2.8. Your example of shooting with the telephoto at even a higher shutter speed than what I typically shoot, with such ugly distortion on the clock, is quite revealing.

Regarding the clock face images, I should point out that I was holding the camera at arms length, with only one hand. One wouldn't normally do this with a tele lens, so you shouldn't get that pronounced effects.

If you are able to keep the camera on your lap, or find other supports, then probably you are ok.

When using the electronic shutter, I usually take a bunch of images after each other, and then look through them to discard those that suffer from rolling shutter artefacts. This usually works well.

Thanks for explaining this. As you mention, I see three uses; Potentially getting slightly better picture of static objects (when shooting fairly wide and at a decent speed) since it eliminates vibration. Ability to shoot more candidly, though with possibly unexpected outcomes, and lastly taking advantage of the unexpected behavior and use it for artistic purposes. In any case, quite a useful feature in my eyes :)

Do you know if it is possible to use the mechanical shutter in M-Mode - for some reason the option is grayed out for me and not sure if I need to do anything specific so it's available when i shoot in manual mode

Do you mean M-mode, like setting the Mode dial on the top to "M"? You should certainly be able to use the mechanical shutter in that mode. I'm not sure why you are getting this option greyed out. Perhaps you have some other feature enabled which prevents you from getting the mechanical shutter mode, but I cannot see what that would be.

yes i meant M-mode as Manual mode on the dial - I have a feeling you are right that i have some other feature enabled which won't let me do it - I suppose that's what i have to figure out. Thanks! at least i know it should definitely work in Manual mode